Abstract

The natural soils of the coastal plains in the southern Arabian region are dominated by saline sands. The organic carbon content of these alkaline sands is 0.54%, equivalent to an organic matter content of 0.9%. The recommended organic matter content for turf and ornamental plant establishment in sand is 8.0%. In the Municipality of Doha in Qatar, the application of sphagnum peat and animal manure or plant-based compost at rates of 200 m3/ha/yr and 150 t/ha/yr are specified for turf production. Application of the selective fungicide Ridomil is also specified to control Pythium root rot. In this trial, a cured, agronomically defined compost was applied as the sole soil conditioner, at a rate calculated to replace all fertilizer phosphorus required during the establishment period for growing Bermuda grass. The rate of application of fertilizer potassium and nitrogen was also adjusted.

The compost was produced from sugar milling byproducts in Queensland (Qld), Australia. The soil conditioning properties of the compost include a water-holding capacity of 72%, a nutrient-holding capacity of 53 mEq/100g (cation exchange capacity), and an organic carbon content of 137 g/L. As a cured compost, the loss on ignition is low (24%), indicating that this compost should have a half-life of years in the soil under Middle Eastern climatic conditions. The trial consisted of the standard Doha Municipal specification, the partial replacement of peat with the Qld compost, the total replacement of peat with one annual application of Qld compost, and the total replacement of peat with one split application of compost to be repeated twice over the establishment period. The turf was irrigated daily and grown for 9 weeks prior to the first cut. The clippings were collected and weighed, the area of yellowed, disease patches in each quadrant was estimated, and the water infiltration rate was recorded as an index of rooting intensity.

The results indicate that the Qld compost successfully replaced the combination of peat and the local compost as an organic soil conditioner for the establishment of turf. At half the volume, the water and nutrient-holding properties conferred to the soil by the Qld compost were equivalent to the full 200 m3/ha application of light peat. In combination with the adjusted fertilizer regime, the application of the Qld compost also reduced the severity of Pythium root rot by 50%.

Many other field trials have been conducted applying compost with the goal of suppressing root disease. However, results are often inconsistent, and at worst, disease severity is increased. The results of this trial prove that the soil conditioning properties of a cured compost can be objectively quantified, enabling the calculation of application rates to replace the use of peat and inorganic soil conditioners. However, if the fertilizer contribution of the compost is not accounted for in the fertiliser management schedule, the desired outcome of reducing disease severity may not be realised.